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Photochromism of Viologens Included in Crown Ether Cavity ¶
Author(s) -
Kuwabara Tetsuo,
Sugiyama Maki,
Nanasawa Masato
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0730469poviic2.0.co2
Subject(s) - photochromism , photochemistry , chemistry , viologen , dication , hexafluorophosphate , molecule , electron transfer , intermolecular force , organic chemistry , ionic liquid , catalysis
The effect of a π‐electron–donating macrocyclic molecule on the photochromic behavior of viologen derivatives was investigated in a thin polymer film. The intermolecular interactions between the viologens and the macrocyclic molecule were investigated in a solution before photoirradiation. In acetone, benzylviologens, N,N ′‐dibenzyl‐4,4′‐bipyridinium hexafluorophosphate (1) and N,N ′‐dibenzyl‐ trans ‐1,2‐bis(4‐pyridinium)ethylene hexafluorophosphate (2) each derived from 4,4′‐bipiyridine and trans ‐1,2‐bis(4‐pyridyl)ethylene, respectively, form an inclusion complex with p ‐benzocrown ether (3) with binding constants of ca 200 M −1 , which was driven by a charge transfer interaction. The peak wavelength of the charge transfer absorption band was at 453 and 421 nm for the inclusion complexes of 1 and 2 with 3, respectively. Upon photoirradiation to the polymer film containing 1, the film changed color from colorless to blue, associated with the reduction of 1 from the dication to the radical cation. The original dication was recovered after 120 min. The addition of 3 into the film containing 1 caused not only the color change from colorless to yellow, associated with the charge transfer interaction between 1 and 3 before photoirradiation, but also an acceleration in the bleaching rate of the photoreduced 1. When p ‐dimethoxybenzene (4) was used as an acyclic analog of 3, a negligible change in the photochromic behavior of 1 was observed. Similar effect of 3 on the photochromic behavior of 2 was observed. These results imply that the π‐electron–donating macrocyclic molecule causes a faster bleaching of photoreduced viologens by forming the inclusion complex.